build: added comments after review (#27721)

PR Close #27721

BUILD.bazel

@@ -69,6 +69,8 @@ nodejs_binary(
 #          "sauce-connect": "https://saucelabs.com/downloads/sc-4.5.3-linux.tar.gz".
 #          On OSX or Windows you'll need to use the appropriate sauce-connect binary.
 # 3) run target with `yarn bazel test --config=saucelabs <target>`
+#    NOTE: --config=saucelabs is required as it makes the SAUCE_XXX environment variables available to
+#          the action. See /.bazelrc.
 karma_web_test(
     name = "test_web_all",
     tags = [

karma-js.conf.js

@@ -145,6 +145,9 @@ module.exports = function(config) {
     browserNoActivityTimeout: 300000,
   }
 
+  // When running under Bazel with karma_web_test, SAUCE_TUNNEL_IDENTIFIER and KARMA_WEB_TEST_MODE
+  // will only be available when `--config=saucelabs` is set. See //:test_web_all target
+  // and /.bazelrc.
   if (process.env['SAUCE_TUNNEL_IDENTIFIER']) {
     console.log(`SAUCE_TUNNEL_IDENTIFIER: ${process.env.SAUCE_TUNNEL_IDENTIFIER}`);